Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

A sensor system for determining a parameter of a fluid medium, e.g., an
intake air mass flowing through a channel, includes at least one sensor
chip situated in the channel for determining the parameter, which sensor
chip is accommodated in a sensor carrier which (i) protrudes into the
channel and (ii) has a leading edge situated transverse to the flow of
the fluid medium. At least one vortex generator is provided, at least in
the region of the leading edge, and configured for forming secondary
flows in the flowing fluid medium in the region of the sensor carrier,
for avoiding or reducing the entry of particles. The secondary flows
extend in a plane essentially perpendicular to the main flow direction of
the fluid medium, e.g., facing away from the sensor area.

Claims:

1. A sensor system for determining at least one parameter of an intake
air mass flowing through a channel of an internal combustion engine,
comprising: at least one sensor chip situated in the channel for
determining the parameter of the intake air mass, wherein the sensor chip
is accommodated in a sensor carrier which protrudes into the channel, the
sensor carrier having a leading edge situated transverse to the flow of
the fluid medium; and at least one vortex generator provided at least in
the region of the leading edge of the sensor carrier, wherein the vortex
generator is configured to form secondary flows in the form of vortices
in the flowing intake air mass in the region of the sensor carrier, and
wherein the secondary flows extend in a plane essentially perpendicular
to the main flow direction of the intake air mass.

2. The sensor system as recited in claim 1, wherein the sensor carrier
essentially defines a plane in the main flow direction of the intake air
mass, and wherein the at least one vortex generator is configured in the
form of at least one projection which protrudes from the plane of the
sensor carrier.

3. The sensor system as recited in claim 2, wherein the at least one
vortex generator is provided at least one of along the leading edge and
along a rear edge of the sensor carrier when viewed in the main flow
direction of the intake air mass.

4. The sensor system as recited in claim 2, wherein the at least one
vortex generator is situated transverse to the main flow direction of the
intake air mass.

5. The sensor system as recited in claim 2, wherein the at least one
vortex generator extends from the leading edge to a rear edge of the
sensor carrier when viewed in the main flow direction of the intake air
mass.

6. The sensor system as recited in claim 3, wherein the at least one
vortex generator is essentially semicircular.

7. The sensor system as recited in claim 1, wherein: the sensor chip has
at least one sensor area which projects into a plane perpendicular to the
flow of the intake air mass: and at least two vortex generators are
situated in such a way that the at least one sensor area is located
between the two vortex generators.

8. The sensor system as recited in claim 7, wherein the at least two
vortex generators are configured to generate multiple vortices such that
the secondary flows, at least in the region of the sensor area, are
provided with vortex axes which are (i) parallel to the main flow
direction of the intake air mass and (ii) in mutually opposite rotational
direction.

9. The sensor system as recited in claim 1, wherein multiple vortex
generators are situated parallel to one another and extend in the main
flow direction of the intake air mass.

10. The sensor system as recited in claim 9, wherein at least one vortex
generator is configured as an indentation at the front edge of the sensor
carrier, the indentation extending in the main flow direction of the
intake air mass.

Description:

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a sensor system for determining at
least one flow property of fluid medium.

[0003] 2. Description of the Related Art

[0004] Numerous methods and devices are known from the related art for
determining at least one flow property of fluid media, i.e., liquids
and/or gases. The flow properties may be basically any given physically
and/or chemically measurable properties which qualify or quantify a flow
of the fluid medium. In particular, a flow rate and/or a mass flow and/or
a volume flow may be involved.

[0005] The present invention is described below in particular with
reference to so-called hot film air mass meters, as described, for
example, in Konrad Reif (publisher): Sensoren im Kraftfahrzeug [Sensors
in Motor Vehicles], Edition 1, 2010, pages 146-148. These types of hot
film air mass meters are generally based on a sensor chip, in particular
a silicon sensor chip, having a sensor diaphragm as a measuring surface
or sensor area over which the flowing fluid medium is able to flow. The
sensor chip generally includes at least one heating element and at least
two temperature sensors which are situated, for example, on the measuring
surface of the sensor chip. A mass flow and/or volume flow of the fluid
medium may be deduced based on an asymmetry of the temperature profile
detected by the temperature sensors, which is influenced by the flow of
the fluid medium. Hot film air mass meters are usually designed as
plug-in sensors which are permanently or replaceably introducible into a
flow tube. For example, this flow tube may be an intake tract of an
internal combustion engine.

[0006] A partial flow of the medium flows through at least one main
channel provided in the hot film air mass meter. A bypass channel is
provided between the inlet and the outlet of the main channel. In
particular, the bypass channel is designed in such a way that it has a
curved section for deflecting the partial flow of the medium which has
entered through the inlet of the main channel, the further course of the
curved section merging into a section in which the sensor chip is
situated. The latter-mentioned section represents the actual measuring
channel in which the sensor chip is situated. A means is provided in the
bypass channel which conducts the flow and counteracts separation of the
flow of the media partial flow from the channel walls of the measuring
channel. Furthermore, in the region of its opening, which points against
the main flow direction, the inlet area of the main channel is provided
with angled or curved surfaces which are designed in such a way that
medium flowing into the inlet area is diverted from the portion of the
main channel leading to the sensor chip. As a result, liquid or solid
particles contained in the medium may not reach the sensor chip due to
their mass inertia, and may soil the sensor chip.

[0007] In practice, these types of hot film air mass meters must meet
numerous requirements and constraints. In addition to the aim of reducing
an overall pressure drop at the hot film air mass meter with the aid of
suitable flow designs, one of the main challenges is to further improve
the signal quality as well as the robustness of such devices with respect
to contamination by oil and water droplets, as well as soot, dust, and
other solid particles. This signal quality relates, for example, to a
mass flow of the medium through the measuring channel leading to the
sensor chip, and optionally to the reduction of a signal drift and the
improvement of the signal-to-noise ratio. The signal drift relates to the
deviation, for example of the mass flow of the medium, in the sense of
changing the characteristic curve relationship between the mass flow
actually occurring and the signal to be emitted within the scope of
calibration during manufacture. For ascertaining the signal-to-noise
ratio, the sensor signals which are output in a rapid time sequence are
taken into account, whereas the characteristic curve drift or signal
drift refers to a change in the mean value.

[0008] In customary hot film air mass meters of the described type, a
sensor carrier having a sensor chip mounted thereon or inserted therein
generally protrudes into the measuring channel. For example, the sensor
chip may be glued into or onto the sensor carrier. The sensor carrier may
form a unit with, for example, a base plate made of metal on which an
electronics system and a control and evaluation circuit in the form of a
printed circuit board may be glued. For example, the sensor carrier may
be designed as a molded-on plastic part of an electronic module. The
sensor chip and the control and evaluation circuit may be connected to
one another via bond connections, for example. The electronic module
produced in this way may, for example, be glued into a sensor housing,
and the entire plug-in sensor may be closed by covers.

[0009] So that the hot film air mass meter is able to deliver an air mass
signal which is as free of interference as possible, flow to the plug-in
sensor and through the measuring channel in the plug-in sensor, and in
particular over the measuring surface of the sensor chip, which is as
uniform as possible, is important. It has been shown that the contour of
the leading edge of the sensor carrier which protrudes into the measuring
channel is of crucial importance for the signal quality of the sensor
system. Thus, for example, it is proposed in published German patent
application document DE 103 455 084 A1 that the leading edge of the
sensor carrier to have a rounded design to improve the flow quality at
the sensor carrier and at the sensor chip, and to avoid pulsing,
nonstationary separations at the surface of the sensor chip.

[0010] Published German patent application document DE 10 2008 042 155 A1
discloses a sensor system for determining at least one parameter of a
fluid medium, in particular an intake air mass of an internal combustion
engine, flowing through a channel. The sensor system has at least one
sensor chip situated in the channel for determining the parameter of the
fluid medium. The sensor chip is accommodated in a sensor carrier which
protrudes into the channel. The sensor carrier has a leading edge,
situated transverse to the flow of the fluid medium, which has at least
one vortex generator that is set up to form longitudinal vortices in the
flowing fluid medium in the region of the sensor carrier. These
longitudinal vortices require an improved intermixture between rapid
fluid more remote from the wall and slower fluid, close to the wall and
in danger of separation, in the region of the sensor carrier. This
intermixture boosts an avoidance of separations. These required
longitudinal vortices are generated by the vortex generator at the
leading edge of the sensor carrier. This reduces the fluctuation in flow
in the region of the sensor carrier, resulting in reduced signal noise
and better reproducibility of the signal.

[0011] Despite the numerous advantages of the methods known from the
related art for reducing the signal noise, these methods are still
capable of improvement with regard to other functional aspects. Thus, due
to the above-described deflection, only lighter particles such as dust,
soot, or water and/or oil droplets, for example, pass into the bypass
channel and into the measuring channel. Due to their mass inertia,
heavier particles exit the hot film air mass meter through the main
channel or bounce against the surrounding walls. The contamination of the
sensor chip and its sensor area by the mentioned lighter particles, in
particular oil and dust, results in an undesirable characteristic curve
drift. Since the heat transfer in the region of the sensor area is
determined primarily by the boundary layer flow on the sensor chip side
of the sensor carrier, and also to a certain degree by the layer remote
from the wall, in the sense of the fluid mechanics definition of a
boundary layer, the flow over these flow regions must be as stable as
possible from a topological standpoint. The contamination by particles
may result in an altered topology over the long term, i.e., a change in
the flow-defining structure at certain points, for example specks of
dust, vortex foci, separation lines, and the like, or may result in a
quantitative change in the flow variables.

BRIEF SUMMARY OF THE INVENTION

[0012] A sensor system for determining at least one flow property of a
fluid medium flowing in a main flow direction is therefore proposed, via
which the disadvantages of known methods and strategies may be at least
largely avoided, and in which a velocity field, in particular on the
sensor chip side of the sensor carrier, which has long-term stability, in
particular with regard to the particle contamination, may be generated.

[0013] The sensor system for determining at least one parameter of a fluid
medium, in particular an intake air mass of an internal combustion
engine, flowing through a channel has at least one sensor chip situated
in the channel for determining the parameter of the fluid medium, the
sensor chip being accommodated in a sensor carrier which protrudes into
the channel, and the sensor carrier having a leading edge situated
transverse to the main flow direction of the fluid medium, at least one
vortex generator being provided at least in the region of the leading
edge and being set up for forming secondary flows, in particular in the
form of vortices, in the flowing fluid medium in the region of the sensor
carrier, in particular in the region of the sensor chip, preferably in
the immediate proximity of a sensor area, in particular of a
micromechanical sensor diaphragm, the secondary flows extending in a
plane essentially perpendicular to the main flow direction of the fluid
medium. When the secondary flow is designed as a vortex, the vortex axis
extends parallel to the main flow direction.

[0014] The sensor carrier may essentially define a plane in the main flow
direction, and the at least one vortex generator may be designed in the
form of at least one projection, such as a web or a ramp, for example,
which protrudes from the plane of the sensor carrier. The at least one
vortex generator may be provided, at least in places, along the leading
edge and/or along a rear edge of the sensor carrier as viewed in the main
flow direction of the fluid medium. The at least one turbulator may be
situated transverse to the main flow direction. The at least one vortex
generator may extend, at least in places, from the leading edge to a rear
edge of the sensor carrier as viewed in the main flow direction of the
fluid medium. The at least one vortex generator may be essentially
semicircular or rectangular. Other cross-sectional shapes are also
conceivable. The sensor chip may have at least one sensor area, and at
least two vortex generators may be situated in such a way that at least
the sensor area projects into a plane perpendicular to the flow of the
fluid medium, situated between the vortex generators. The at least two
vortex generators may be designed in such a way that due to multiple
vortices, the secondary flows, at least in the region of the sensor area,
are provided with the particular vortex axis parallel to the main flow
direction of the fluid medium and in the mutually opposite rotational
direction, i.e., with oppositely directed vortex axes. Multiple vortex
generators may be situated extending in the main flow direction and
parallel to one another. At least one vortex generator may be designed as
an indentation in the sensor carrier, preferably at the front edge of the
sensor carrier which extends in the main flow direction. At least one
indentation in the sensor carrier may extend in the main flow direction
and, projected into the plane perpendicularly to the main flow direction,
may be located laterally adjacent to the sensor area.

[0015] Within the scope of the present invention, the main flow direction
is understood to mean the local flow direction of the fluid medium at the
location of the sensor or of the sensor system, whereby, for example,
local irregularities such as turbulences may continue to be disregarded.
In particular, the main flow direction may thus be understood to mean the
local averaged transport direction of the flowing fluid medium.

[0016] Within the scope of the present invention, "transverse to the main
flow direction" is understood to mean perpendicular or essentially
perpendicular, for example having an orientation which deviates by no
more than 10° from the vertical with respect to the local main
flow direction. Within the scope of the present invention, "essentially"
is understood to mean an orientation which deviates by no more than
20°, preferably by no more than 10°, and particularly
preferably by no more than 5°, and/or by no more than 20%, in
particular by no more than 10%, and particularly preferably by no more
than 5%, of the particular stated reference direction, reference plane,
or reference shape. Thus, for example, an "essentially parallel"
orientation is an orientation which deviates from parallelism by no more
than the stated tolerances.

[0017] Within the scope of the present invention, according to the fluid
mechanics, secondary flow is understood to mean a comparatively low
velocity, i.e., the secondary velocity, in addition to the main flow in a
plane essentially transverse to the main flow direction.

[0018] Within the scope of the present invention, according to the fluid
mechanics, a vortex is understood to mean a complete or partially
circular flow or approximately circular flow of a fluid. Within the scope
of the present invention, the vortex axis is understood to mean the axis
about which the circular flow runs. This axis may extend, for example,
parallel to a vortex vector of the vortices. To generate the vortices of
the stated type, which are also referred to below as transverse vortices,
since the mentioned vortex axis of the vortices extends essentially
parallel to the main flow direction of the fluid, and the secondary flows
of the vortex form as circular flow or approximately circular flow around
the vortex axis, the vortex generator may have various designs. Thus, the
vortex generator may be set up in such a way, for example, that at least
two adjacent regions having different static pressures exist in at least
one plane perpendicular to the main flow direction. This may be achieved
in such a way, for example, that the vortex generator is set up to
generate at least two adjacent regions having different flow cross
sections, for example via different constrictions in a region through
which the flow passes, so that the flow passes through these regions at
different velocities according to the Bernoulli equation, and different
pressures are formed in these regions. The formation of the secondary
flows may then be a result of a compensation for these different
pressures. For example, the vortex generator may be designed in such a
way that at least two sections exist which have a different distance
between the leading edge and a wall of the channel, i.e., sections having
different flow cross sections.

[0019] These types of transverse vortices may be visualized, for example,
with the aid of numerical fluid mechanics simulations in order to
visually represent their existence. Alternatively, the vortices may be
visualized, for example, with the aid of smoke and/or so-called smoke
wire visualization, for example using a camera that records smoke
turbulences in the flow and/or downstream from the vortex generator. In
smoke wire visualization, a wire is provided with an oil-containing
substance, for example, and is heated. During heating of the wire the
substance evaporates, and upon separating from the wire immediately
condenses in the surroundings, and the individual condensing particles
become visible. The flow lines composed of these particles are then
individually detectable, thus allowing good observation of the flow
profile. Another method for visualizing the flow profile is the so-called
particle image velocimetry (PIV). Flow visualization by PIV is based on
the correlation of two digital recordings, offset in time, of a particle
cloud in the light section. The result of the correlation is a
two-dimensional vector field. The flow profile and the flow rate may be
deduced on this basis.

[0020] Within the scope of the present invention, "in places" is
understood to mean an arrangement which does not extend completely along
or over the particular stated length or extension of the reference
component or the direction, but, rather, which is provided only in
sections or partially. In particular, the arrangement itself may have
interruptions or recesses so that it has a segmented design.

[0021] Within the scope of the present invention, the sensor carrier may
be completely or partially designed as a printed circuit board or may be
part of a printed circuit board. For example, the printed circuit board
may have an extension which forms the sensor carrier and protrudes into
the channel, for example the measuring channel of a hot film air mass
meter. The remaining portion of the printed circuit board may be
accommodated, for example, in an electronics compartment, or in a housing
of the sensor system or of a plug-in sensor of the sensor system.

[0022] Within the scope of the present invention, a printed circuit board
is generally understood to mean an essentially plate-shaped element which
may also be used as a support for electronic structures, for example
circuit board conductors, terminal contacts, or the like, and which
preferably also has one or more of these types of structures. In
principle, at least slight deviations from the plate shape are also
considered, and conceptually are included with same. The printed circuit
board may be made, for example, of a plastic material and/or a ceramic
material, an epoxy resin, for example, in particular a fiber-reinforced
epoxy resin. In particular, the printed circuit board may be designed,
for example, as a printed circuit board having circuit board conductors,
in particular printed circuit board conductors (PCB).

[0023] In this way, the electronic module of the sensor system may be
greatly simplified, and a base plate and a separate sensor carrier, for
example, may be dispensed with. The base plate and sensor carrier may be
replaced by a single printed circuit board on which, for example, a
control and evaluation circuit of the sensor system may also be
completely or partially situated. This control and evaluation circuit of
the sensor system is used to control the at least one sensor chip and/or
the evaluation of the signals generated by this sensor chip. Thus, by
combining the mentioned elements, the complexity of manufacturing the
sensor system may be significantly reduced, and the space requirement for
the electronic module may be greatly reduced.

[0024] The sensor system may in particular have at least one housing, the
channel being provided in the housing. For example, the channel may
include a main channel and a bypass channel or measuring channel, whereby
the sensor carrier and the sensor chip may be situated in the bypass
channel or measuring channel, for example. In addition, the housing may
have an electronics compartment which is separate from the bypass
channel, the electronic module or the printed circuit board essentially
being accommodated in the electronics compartment. The sensor carrier may
then be designed as an extension of the printed circuit board which
protrudes into the channel. In contrast to the complicated electronic
modules known from the related art, this system is comparatively easy to
implement technically.

[0025] In particular in the case in which a printed circuit board is used
as the sensor carrier, but also in other cases and/or when other media
are used as the sensor carrier, the sensor carrier may be designed, at
least partially, as the multilayer sensor carrier. Thus, the sensor
carrier may be designed in a so-called multilayer technique, and have two
or more carrier layers joined together. For example, these carrier layers
may once again be made of a metal, a plastic, or a ceramic material or a
composite material, and joined together using joining techniques, for
example gluing.

[0026] in this case, in which a multilayer technique is used having
multiple sensor layers of the sensor carrier, the leading edge may have
an at least partially stepped design against the main flow direction of
the fluid medium as the result of different dimensioning of the carrier
layers. The profiles may thus be implemented in at least an approximately
stepped manner. For example, profiles in a section plane perpendicular to
the extension plane of the sensor carrier may thus be provided with a
shape that is rectangular or, approximated by a stepped shape, at least
approximately circular, rounded, or wedge-shaped. The sensor chip may be
situated on or in the sensor carrier in such a way that it is oriented
perpendicularly to the local main flow direction. For example, the sensor
chip may have a rectangular design, one side of this rectangle being
perpendicular or essentially perpendicular, for example with an
orientation that deviates by no more than 10 degrees from the vertical
with respect to the local main flow direction.

[0027] The sensor chip may be electrically contacted via at least one
electrical connection. For example, the sensor carrier, in particular a
printed circuit board which forms the sensor carrier or an extension of
this printed circuit board, may have one or multiple printed conductors
and/or contact pads which are connected to corresponding contacts on the
sensor chip, for example with the aid of a bonding process. In this case,
the electrical connection may be protected by at least one cover and be
separated from the fluid medium. This cover may in particular be designed
as a so-called "glob top," for example as plastic drops and/or adhesive
drops, which covers the electrical connection, for example the bond
wires. In particular, influences on the flow by the electrical connection
may also be avoided in this way, since the glob top has a smooth surface.
In addition, the sensor chip may have at least one sensor area. This
sensor area may be, for example, a sensor surface made, for example, of a
porous ceramic material, and/or in particular may be a sensor diaphragm.

[0028] With the aid of the present invention, changes in the velocity
field may be reduced compared to a new or initial state of the sensor
system; in particular, however, regions of low velocity in the particle
gathering area of the sensor area may be avoided or reduced. Over the
service life of the sensor system, such low-velocity regions may be used
as a collection point for increasingly larger numbers of particles. Since
the particles change the tendency toward contamination and the heat
transfer to the air, the following effects in particular are achieved by
individual measures or by a combination of measures. The growth of the
boundary layer due to contamination is avoided or at least reduced, since
an effective reduction in the flow pulse in the vicinity of the sensor
area is thus achieved. The vortex foci, specks of dust, or collection
points which form in the region around the sensor area are avoided or at
least reduced. Separations on the side of the sensor carrier facing the
sensor chip as well as on the side of the sensor carrier facing away from
the sensor chip are avoided or at least reduced. In addition, the aim is
to avoid or at least reduce low-velocity regions which result from other
causes. Furthermore, the measures are also suitable for nonstationary
reverse flow states, i.e., pulsation in the intake tract. Via appropriate
designs at the front and/or rear edge of the sensor carrier, the aim
ideally is to adapt the bandwidths of the velocity fields to one another
during the forward and reverse flow. As a side effect, the stabilizing
measures result in smaller velocity fluctuations for the instantaneously
measured mean value in the region of the sensor area, resulting in lower
signal noise and better reproducibility.

[0029] With the aid of the present invention, for reducing the tendency
toward particle contamination, secondary velocities may be generated or
induced in the main flow, and/or low-velocity regions may be avoided on
and in the immediate proximity of the sensor area, in particular of the
micromechanical sensor diaphragm.

[0030] In addition, a topologically more exact definition of the flow
field, including the boundary layer flow in the immediate proximity of
the sensor area, in particular of the sensor diaphragm, is possible,
i.e., avoidance of characteristics of the flow-defining structures, which
change with the mass flow or flow states, such as, for example,
stagnation points and saddle points, separation lines, vortex foci,
variation of the wall shear stress over time, and the like. The avoidance
of or reduction in the particle accumulation as well as the harmonization
of the flow over the sensor area are achieved by the measures according
to the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG. 1 shows a perspective illustration of a sensor system.

[0032] FIG. 2 shows a view of a sensor carrier together with a sensor chip
in a channel, viewed in the main flow direction.

[0033] FIG. 3 shows a top view of a sensor carrier together with a sensor
chip (back side) in a channel.

[0034] FIG. 4 shows an enlarged top view of an unclosed sensor housing
together with the channel structure, and of the sensor carrier together
with the sensor chip, and a schematic illustration of the flow through
the channel.

[0035] FIG. 5 shows an enlarged illustration of an electronic module of
the sensor system, together with the sensor carrier and the installed
sensor chip.

[0036] FIG. 6A shows a perspective view of a ramp pair for generating a
secondary flow in a rectangular channel.

[0037] FIG. 6B shows a top view of the ramp pair in the rectangular
channel, and a schematic illustration of the distribution of the static
pressure.

[0038] FIG. 7A shows a perspective view of a secondary flow field
downstream from the ramp pair in the rectangular channel.

[0039] FIG. 7B shows a view of the secondary flow field downstream from
the ramp pair in the rectangular channel, viewed in the main flow
direction.

[0040] FIG. 7C shows another perspective view of the ramp pair, with an
illustration of the velocities and flow lines.

[0041] FIG. 7D shows an enlarged detail of the secondary flow field in the
region of the transition between the ramps.

[0042]FIG. 8A shows a top view of sensor chips of two different sensor
carriers, and the illustration of a temperature distribution in the main
flow direction, without chip heating.

[0043] FIG. 8B shows a top view of sensor chips of two different sensor
carriers, and the illustration of two temperature distributions in the
main flow direction, with chip heating.

[0044] FIG. 9A shows a top view of a first specific embodiment of a sensor
carrier.

[0045] FIG. 9B shows a view of the first specific embodiment of the sensor
carrier, viewed in the main flow direction.

[0046] FIG. 10 shows a top view of a second specific embodiment of a
sensor carrier.

[0047] FIG. 11 shows a top view of a third specific embodiment of a sensor
carrier.

[0048] FIG. 12 shows a top view of a fourth specific embodiment of a
sensor carrier.

[0049] FIG. 13 shows a top view of a fifth specific embodiment of a sensor
carrier.

[0050] FIG. 14 shows a view of a sixth specific embodiment of a sensor
carrier, viewed in the main flow direction.

[0051] FIG. 15 shows a view of a seventh specific embodiment of a sensor
carrier, viewed in the main flow direction.

[0052] FIG. 16 shows a perspective view of an eighth specific embodiment
of a sensor carrier.

[0053] FIG. 17 shows a view of a ninth specific embodiment of a sensor
carrier, viewed in the main flow direction.

[0054]FIG. 18A shows two results of a flow simulation, using different
air mass flows, without a sensor system according to the present
invention, in which the velocity field in a sensor area, the wall shear
stress on the sensor carrier, the isosurface of the vortex strength, and
the wall flow lines are illustrated.

[0055] FIG. 18B shows enlarged illustrations of the velocity fields in
FIG. 18A, viewed in the main flow direction.

DETAILED DESCRIPTION OF THE INVENTION

[0056] FIG. 1 shows a sensor system 10 for determining a parameter of a
fluid medium. In the present exemplary embodiment, sensor system 10 is
designed as a hot film air mass meter, and includes a plug-in part 12
which may plugged into a flow tube, for example, in particular an intake
tract of an internal combustion engine. A channel structure 14, apparent
in FIG. 1 or FIG. 4, is accommodated in plug-in part 12, through which a
representative quantity of the fluid medium is able to flow through an
inlet opening 16, which in the inserted state points toward a main flow
direction 18 of the fluid medium.

[0057] FIG. 4 shows an enlarged detail of plug-in part 12 in the region of
the channel structure. Channel structure 14 has a main channel 20 which
opens into a main flow outlet 22 on the bottom side, relative to the
illustration in FIG. 1, of plug-in part 12, and a bypass channel or
measuring channel 24 which branches off from main channel 20 and opens
into a bypass channel or measuring channel outlet 26 likewise situated on
the bottom side, relative to the illustration in FIG. 1, of plug-in part
12, as is apparent from FIG. 4.

[0058] A sensor carrier 28 in the form of a wing protrudes into measuring
channel 24, as illustrated in FIG. 1 and FIG. 2, for example. FIG. 2
shows the view of sensor carrier 28 in measuring channel 24 in the main
flow direction. FIG. 3 shows a top view of the arrangement of sensor
carrier 28 in measuring channel 24. A sensor chip 30 is embedded in this
sensor carrier 28 in such a way that the fluid medium flows over a sensor
diaphragm 32, which is designed as a sensor area of sensor chip 30. As is
apparent in particular in FIG. 5, sensor carrier 28 together with sensor
chip 30 is an integral part of an electronic module 34, illustrated in
enlarged scale. This electronic module 34 has a bent base plate 36 as the
sensor carrier, and a printed circuit board 38 mounted, for example
glued, thereon, having a control and evaluation circuit 40. Sensor
carrier 28 may be molded onto base plate 36, for example as a plastic
component.

[0059] The sensor chip is electrically connected to control and evaluation
circuit 40 via electrical connections 42, in the present case designed as
wire bonding, as is apparent in particular from FIG. 5. Resulting
electronic module 34 is introduced, for example glued, into an
electronics compartment 44 in a housing 46 of plug-in part 12 in which
channel structure 14 is also provided, as is apparent in FIG. 1. This is
carried out in such a way that sensor carrier 28 protrudes into channel
structure 14. Electronics compartment 44 and channel structure 14 are
subsequently closed by lid 48.

[0060] Sensor carrier 28, which is molded onto base plate 36 as an
injection-molded component, for example, or which may be an integral part
of base plate 36 or printed circuit board 38, is provided with a leading
edge 50, which may have a rounded design, as is apparent from FIG. 2, for
example. For example, this leading edge 50 may be implemented similarly
to an airfoil with a constant contour. The specific embodiments of sensor
carrier 28 according to the present invention are described in greater
detail below. First, however, the fluid mechanics correlations of
cross-sectional changes in a channel, for example measuring channel 24,
with the aid of vortex generators, for example ramps, steps, or blocks,
are explained in order to clarify the conceptual approach, underlying the
present invention, of the various specific embodiments of the sensor
carrier. In particular, the explanation as an example is intended to
illustrate the principle of using cross-sectional changes of certain
sections or regions in a channel to intentionally form secondary flows
such as longitudinal vortices, for example.

[0061] As an example, FIGS. 6A and 6B show a ramp pair 52, 54 of different
heights in a rectangular channel 56, FIG. 6A illustrating an arrangement
in perspective view with flow from the left, and FIG. 6B illustrating a
corresponding top view with a schematic illustration of the distribution
of the static pressure. Thus, main flow direction 18 is parallel to the
longitudinal axis of rectangular channel 56 from left to right according
to the illustrations in FIGS. 6A and 6B. According to the Bernoulli
equation, the static pressure decreases in the region of a flow which is
accelerated to a higher velocity. The flow is accelerated to a greater
degree in the region of higher ramp 52 than in the region of lower ramp
54. Accordingly, the static pressure is lowered to a greater degree in
the region of higher ramp 52. In relative terms, the static pressure in
the region of lower ramp 54 is greater than that in the region of higher
ramp 52. This is indicated by the symbols "+" and "-" in FIG. 6B. Due to
the ramp geometries and the different static pressures, velocity
components, also referred to as secondary velocity components, result in
the plane perpendicular to main flow direction 18, and vortices 55A, 55B
form downstream from ramps 52, 54, respectively, as is apparent from FIG.
7A or FIG. 7B, for example, in order to equalize the pressures. In
particular, the vortex axis of vortices 55A, 55B extends essentially
parallel to main flow direction 18. In particular, two vortices 55A, 55B
result in this arrangement, a larger vortex 55A having a clockwise
rotational direction and extending essentially over the entire cross
section of channel 56, and a smaller vortex 55B, in a region downstream
from larger ramp 52 having a counterclockwise rotational direction, and
whose profile in terms of surface area or extent of spreading being
essentially identical to the cross-sectional area of higher ramp 52.

[0062] FIG. 7A shows a perspective view of this type of velocity field of
vortices 55A, 55B in a plane perpendicular to main flow direction 18, and
FIG. 7B shows a top view of this projected velocity field plane of these
vortices 55A, 55B downstream from ramp pair 52, 54, respectively, as a
result of a numerical flow simulation. The regions of the particular
velocity fields are surrounded by thin lines for better
distinguishability and delimitability. The lengths of the vectors of the
velocity field indicate the particular magnitude of the velocity
projected into the plane, a greater length of a vector indicating a
higher velocity.

[0063] A number of effects may be identified here. Areas of low flow rate
are located directly downstream from such projections, for example steps,
ramps, and the like. The component in main flow direction 18 is much
smaller than in the core flow region, and so-called "dead water areas"
having small velocity components exist which may even point against the
main flow, i.e., back-flow in negative main flow direction 18, as shown
in FIG. 7C, for example. FIG. 7C shows the velocities and the flow lines
in a perspective side view at the level of the particular ramp, the
differently dotted regions of the flow lines indicating the particular
magnitude of the velocity. The illustration in FIG. 7C also shows a
coordinate system, main flow direction 18 being indicated on the axis
denoted by X, and the axes denoted by Y and Z defining a plane
perpendicular to main flow direction 18. According to the above
definition, an orientation transverse to main flow direction 18 is
therefore located in the Y-Z plane. The secondary velocities in the
stated plane perpendicular to the main flow, i.e., in the Y-Z plane of
FIG. 7C, are also low. Thus, there is a higher probability of
accumulation of particles in such low-velocity regions. The arrangement
of micromechanical sensor diaphragm 32 would therefore most probably
result in increased contamination and characteristic curve drift. In
addition, above-mentioned vortices 55A, 55B having a vortex axis
essentially parallel to the main flow direction result downstream from or
behind larger ramp 52. At the transition to lower ramp 54, an upwardly
directed secondary flow of larger vortex 55A with respect to larger ramp
52 exists, which in this region is partially overlapped by the secondary
flow of smaller vortex 55B or is intermixed with same, and which has the
same direction, or at a further distance from the wall has a strong
secondary flow upward, i.e., in the direction of the elevation of ramps
52, 54, and facing away from lower ramp 54, as shown in FIG. 7D.

[0064] FIG. 7D schematically shows a detail of the transition from such a
higher projection to a lower projection, projected into the stated plane
perpendicular to main flow direction 18, and one possible arrangement of
a micromechanical sensor diaphragm 32 in the region of the secondary
velocities of larger vortex 55A. On account of the secondary flow, which
is present even at low velocities, there should be no accumulation of
particles in the region of sensor diaphragm 32; instead, the particles
should be carried away from sensor diaphragm 32 due to generated vortex
55A. Thus, in overall rectangular channel 56 at least a pronounced
secondary flow results in the plane perpendicular to main flow direction
18 due to ramps 52, 54, which are large relative to the channel
dimensions. Due to the size ratios in the bypass channel of the hot film
air mass meter, such a clockwise secondary flow of larger vortex 55A
according to the illustration in FIG. 7D is distributed not over the
entire sensor carrier, but, rather, only locally in the region of
micromechanical sensor diaphragm 32, since the dimensions of the
corresponding interfering bodies are only of the order of magnitude of
sensor carrier 28, possibly only of the order of magnitude of sensor chip
30 or of micromechanical sensor diaphragm 32. Therefore, the resulting
secondary flows should not be confused with turbulent, additional
velocity fluctuations which may also form over the entire sensor carrier,
transverse to the main flow direction, but which have significantly
smaller absolute values of velocity compared to the above-described
secondary flows. The present invention is therefore directed to
influencing the path of the light particles which are not filtered out by
the deflection by centrifugal force or by adherence to the bypass channel
walls, or which have extreme deviations from main flow direction 18 due
to bouncing against the bypass channel walls. The aim is to keep such
particles away from sensor diaphragm 32 as the result of the
geometrically induced secondary velocities.

[0065] The reduction in the tendency toward contamination due to the
explained principle and the specific embodiments of sensor carrier 28
described below requires a certain flow rate. Using the measures
described below, there is only a very limited possibility of preventing
contamination due to oil vapor at very low velocities, which occurs, for
example, as the result of crankcase venting when a motor vehicle is
switched off. For this case, so-called chip heating may be provided. FIG.
8A shows two top views of a sensor chip 30 of two different sensor
carriers 28 without chip heating, main flow direction 18 being indicated
by an arrow, and a temperature distribution over main flow direction 18
being plotted on the axis denoted by X. The top views of sensor chips 30
clearly show the accumulations of oil droplets, in particular in the
region around sensor diaphragm 32, in the lower illustration the oil
droplets being smaller or more finely distributed compared to the upper
illustration. FIG. 8B shows two top views of a sensor chip 30 of two
different sensor carriers 28 with chip heating, main flow direction 18
being indicated by an arrow, and two associated temperature distributions
as the result of different heating modes over main flow direction 18
being plotted on the axis denoted by X. When the chip heating is switched
on, a reduction in the entry of oil is clearly apparent, as is
discernible from FIG. 8B, for example. In normal operation of an internal
combustion engine, for example an internal combustion engine of a motor
vehicle, primarily dust and soot particles adhere to the oil droplets,
resulting in an altered heat transport, and therefore, in a
characteristic curve drift. The aim of the present invention is not to
avoid oil accumulation during crankcase venting when the engine is
switched off, but, rather, the subsequent accumulation of particles.
However, it is pointed out that aerodynamic forces counteract the
mechanisms of oil contamination when the engine is switched off, even at
very low flow rates. The stated possibility for reducing the entry of oil
by chip heating is mentioned only as one optional, additional possibility
for reducing the particle accumulation.

[0066] The individual specific embodiments of sensor carrier 28, using the
principle of the targeted change in flow with the aid of design measures,
are described in detail below. Use of the change in geometry is
conceivable for the inflow side, which is important for normal operation,
as well as for the outflow side, which is important for pulsing flow.

[0067] FIG. 9A shows a top view of a first specific embodiment of a sensor
carrier 28 according to the present invention, and FIG. 9B shows a side
view, viewed in main flow direction 18. According to the first specific
embodiment, two vortex generators 58 which are set up to generate
secondary flows or to induce same in the main flow direction, and which
therefore may also be referred to as secondary flow generators, are
provided, and as cuboidal and/or web-shaped projections protrude
essentially perpendicularly from the plane of sensor carrier 28. In
particular, vortex generators 58 are situated on sensor carrier 28, in
the region of leading edge 50, in such a way that sensor diaphragm 32
projects into the plane perpendicularly to main flow direction 18,
situated between vortex generators 58, as is apparent from the
illustration in FIG. 9B. According to the projected illustration in FIG.
9B, one vortex generator 58 is thus located to the left of sensor
diaphragm 32, and the other vortex generator 58 is located to the right
of sensor diaphragm 32. In the illustration shown in FIG. 9A, vortex
generators 58 have a relatively small depth; i.e., their dimension viewed
in main flow direction 18 is relatively small compared to their other
dimensions. Downstream from these vortex generators 58 as viewed directly
in main flow direction 18, low-velocity regions 59, indicated by two
ellipses, result on sensor carrier 28. Vortex generators 58 generate
regions of higher velocity and lower pressure due to the thickening of
the boundary layers in their trailings to the left and right of sensor
diaphragm 32, and therefore slightly farther downstream than the regions
indicated by the ellipses, so that the flow region upstream from and
above sensor diaphragm 32, starting from the center of sensor diaphragm
32, has outwardly directed secondary velocities. In addition, oppositely
rotating vortices 55 result to the left and right of sensor diaphragm 32
whose vortex axes extend essentially parallel to the main flow direction
and which drive the particles from sensor diaphragm 32 outwardly and
upwardly in each case, i.e., into the more rapid main flow. The height
and the width, the extension in main flow direction 18, or the position
of the inner edge of the vortex generators relative to the position of
sensor diaphragm 32 may vary.

[0068] FIG. 10 shows an illustration of a second specific embodiment which
corresponds to the illustration in FIG. 9A. The second specific
embodiment represents a modification of the first specific embodiment.
Only the differences from the first specific embodiment are described
below, and identical components are provided with the same reference
numerals. In comparison to the first specific embodiment, vortex
generators 58 have a greater depth in main flow direction 18. Vortex
generators 58 of the second specific embodiment bring about similar
effects as those described for the first specific embodiment. The
strength of the secondary flow should increase compared to the first
specific embodiment.

[0069] A third specific embodiment is shown in FIG. 11 in a top view. Only
the differences from the preceding specific embodiments are described
below, and identical components are provided with the same reference
numerals. In the third specific embodiment a plurality of vortex
generators 58 is provided, the vortex generators being situated on sensor
carrier 28, parallel to one another in main flow direction 18, and
protruding essentially perpendicularly from the plane of sensor carrier
28. Vortex generators 58 are designed as cuboidal and/or web-shaped
projections, for example. In addition, vortex generators 58 which are
located in the region of sensor chip 30 in a direction transverse to main
flow direction 18, viewed in or parallel to the plane of sensor carrier
28, each have an interruption or a recess within which sensor chip 30 is
situated. In particular, vortex generators 58 which have an interruption
or a recess do not terminate in flush alignment with sensor chip 30, but,
rather, are located at a small distance from sensor chip 30 in and
against main flow direction 18. In the remaining regions of sensor
carrier 28, vortex generators 58 have a consistent design from leading
edge 50 to the rear edge of sensor carrier 28, viewed in main flow
direction 18. A single or multiple interruption is conceivable. In the
third specific embodiment, vortex generators 58 have a relatively small
width: i.e., their dimension transverse to main flow direction 18 in or
parallel to the plane of the sensor carrier is relatively small compared
to their other dimensions. Alternatively or additionally, grooves and/or
protruding steps may be provided, which due to their consistency conduct
the flow, and which in particular in the case of pulsation are designed
to prevent uncontrolled lateral entry of particles. At the same time,
these types of grooves are used for runoff of any oil which is deposited
despite chip heating. The height of the protruding steps may be constant,
or may also increase in a curved manner in main flow direction 18, or in
some cases may assume other suitable profiles, in particular in the
vicinity of sensor diaphragm 32.

[0070] FIG. 12 shows an illustration of a fourth specific embodiment
corresponding to the illustration in FIG. 11. The fourth specific
embodiment represents a modification of the third specific embodiment.
Only the differences from the third specific embodiment are described
below, and identical components are provided with the same reference
numerals. Vortex generators 58 have a greater width compared to the third
specific embodiment. In addition, vortex generators 58, which have an
interruption or a recess, terminate in flush alignment with sensor chip
30. Vortex generators 58 in the fourth specific embodiment bring about
similar effects as those described for the third specific embodiment.

[0071] A fifth specific embodiment is shown in FIG. 13 in a top view. Only
the differences from the preceding specific embodiments are described
below, and identical components are provided with the same reference
numerals. In the fifth specific embodiment, two vortex generators 58
which are designed as spaced-apart milled grooves or recesses, for
example having a rectangular, semicircular, or square design in a top
view, in sensor carrier 28 are located in the region of leading edge 50.
In particular, vortex generators 58 are situated on sensor carrier 28 in
the region of leading edge 50 in such a way that sensor diaphragm 32,
which projects into a plane perpendicular to main flow direction 18, is
situated between vortex generators 58.

[0072] Due to the stagnation point effect of milled grooves 58, the fifth
specific embodiment produces a thicker boundary layer in the trailings of
milled grooves 58, downstream from milled grooves 58 at the leading edge,
compared to the flow course outside milled grooves 58 at leading edge 50,
which is rounded similar to an airfoil profile, and thus has the same
effect as an actually present step geometry according to the
above-described specific embodiments. Secondary velocities and oppositely
rotating vortices 55, each having a vortex axis parallel to main flow
direction 18, likewise form as described above.

[0073] A sixth specific embodiment is shown in FIG. 14 in a view in the
main flow direction. Only the differences from the preceding specific
embodiments are described below, and identical components are provided
with the same reference numerals. In the sixth specific embodiment,
similarly to the fourth specific embodiment, two vortex generators 58 are
provided on sensor carrier 28, parallel to one another in main flow
direction 18, and protrude essentially perpendicularly from the plane of
sensor carrier 28. Vortex generators 58 are designed, for example, as
cuboidal and/or web-shaped projections. In particular, vortex generators
58 are situated on sensor carrier 28 in such a way that sensor diaphragm
32, which projects in a plane perpendicular to main flow direction 18, is
situated between vortex generators 58. In the sixth specific embodiment,
vortex generators 58 are comparatively high and wide. In the sixth
specific embodiment shown in FIG. 14, not only variations in the position
and the number, but also asymmetrical arrangements due to the incoming
flow which concern the width, height, or height profile are conceivable.
In addition, other shapes are conceivable in the shape transverse to main
flow direction 18. For example, vortex generators 58 shown as projections
may also be semicircular, or be provided with radii at both edges.

[0074] FIG. 15 shows an illustration of a seventh specific embodiment
corresponding to the illustration in FIG. 14. The seventh specific
embodiment represents a modification of the sixth specific embodiment.
Only the differences from the sixth specific embodiment are described
below, and identical components are provided with the same reference
numerals. In comparison to the sixth specific embodiment, vortex
generators 58 have a smaller width and height. Vortex generators 58 in
the seventh specific embodiment bring about similar effects as described
for the sixth specific embodiment, and may likewise have the design
alternatives described therein.

[0075] FIG. 16 shows an illustration of an eighth specific embodiment in a
perspective top view. The eighth specific embodiment represents a
modification of the sixth or seventh specific embodiment. Only the
differences from the sixth or seventh specific embodiment are described
below, and identical components are provided with the same reference
numerals. In comparison to the sixth or seventh specific embodiment, the
two vortex generators 58 are curved in main flow direction 18; i.e.,
their height increases in main flow direction 18, viewed from leading
edge 50, toward sensor chip 30, and downstream from sensor chip 30 the
height decreases in main flow direction 18 toward the rear edge. In
particular, a vortex generator 58 has a consistent design, and that
vortex generator 58 which is located in the region of the sensor chip 30,
in a direction transverse to main flow direction 18, viewed in or
parallel to the plane of sensor carrier 28, has an interruption or a
recess within which sensor chip 30 is situated. Vortex generators 58 in
the eighth specific embodiment bring about similar effects as described
for the sixth specific embodiment, and may likewise have the design
alternatives described therein.

[0076] A ninth specific embodiment is shown in FIG. 17 in a side view in
main flow direction 18. The ninth specific embodiment represents a
modification of the sixth or seventh specific embodiment. Only the
differences from the sixth or seventh specific embodiment are described
below, and identical components are provided with the same reference
numerals. In the ninth specific embodiment, in addition to the two vortex
generators 58, two grooves 60 are provided which extend in the sensor
carrier between vortex generators 58 from leading edge 50 to the rear
edge of sensor carrier 28, viewed in main flow direction 18, in such a
way that sensor diaphragm 32 is located between grooves 60. This takes
into account the fact that oil accumulations upstream and downstream from
sensor diaphragm 32 change the boundary layer in the immediate proximity
of sensor diaphragm 32. Changes in the heat transport from sensor
diaphragm 32 into the air are therefore to be expected. With the correct
design, grooves 60 in the uncontaminated state should play no role for
the boundary layer, since they contain only low-pulse fluid. In the case
of contamination, however, grooves 60 should receive oil droplets and
prevent actual local thickening of the effective flow contour in front of
or upstream from sensor diaphragm 32.

[0077] The embodiments of sensor carrier 28 according to the present
invention may have other appropriate modifications or design
alternatives. In particular, it is explicitly emphasized that
combinations of the described geometries of vortex generators 58 are also
possible.

[0078]FIG. 18A shows two results of a flow simulation using different air
mass flows, none of the embodiments according to the present invention
having been used. Thus, the geometric configuration shows the flow
situation without secondary flows induced according to the present
invention. In particular, the particular velocity field in a sensor area
32, the wall shear stress on sensor carrier 28, the isosurface of vortex
strength 64, and wall flow lines 66 are shown for the simulation results.
In particular, the left illustration in FIG. 18A shows a sensor carrier
28 over which an air mass flow of 90 kg/h flows, and the right
illustration shows a sensor carrier 28 over which an air mass flow of 200
kg/h flows. Main flow direction 18 extends in the negative direction of
the shown Z axis, and the surface of sensor carrier 28 is situated in a
plane defined by the Y axis and the Z axis. Also shown is the particular
velocity field in the immediate proximity of a sensor area, such as a
sensor diaphragm 32, for example, in the plane perpendicular to main flow
direction 18. The particular velocity fields are illustrated in enlarged
scale in FIG. 18B. The differently dotted regions indicate the different
velocities, a denser dot pattern corresponding to a higher velocity. The
flows show clearly different velocity fields at the level of sensor
diaphragm 32, clearly different wall shear stresses 62 on the sensor
carrier, clear differences in the isosurfaces of vortex strength 64, and
deviations in the variation of the wall flow lines 66 as the result of
numerical flow simulations for the two cases of 90 kg/h and 200 kg/h. For
example, in the example of a flow of 90 kg/h, wall shear stresses 62 in
the positive direction of the X axis upstream from sensor area 32 are
relatively straight and are apparent as light stripes, while wall shear
stresses 62 in the example of a flow of 200 kg/h assume an approximately
sinusoidal curve in the stated direction. The embodiments according to
the present invention are intended to reduce the flow differences for
different air mass flows. For example, the deviations with regard to the
design of wall shear stresses 62 and the velocity profile shown in FIG.
18B should be reduced between the flow case having 90 kg/h and the case
having 200 kg/h.